1. Field of the Invention
The present invention relates to a method of producing a surface acoustic wave device for use in a resonator, a bandpass filter, or other such apparatus, and more particularly, to a method of producing an edge reflection type surface acoustic wave device utilizing an SH type surface acoustic wave.
2. Description of the Related Art
In recent years, different types of edge reflection type surface acoustic wave devices for which no reflectors are required have been proposed. FIG. 3 is a perspective view showing an edge reflection type surface acoustic wave resonator as an example of the above-described edge reflection type surface acoustic wave devices. In an edge reflection type surface acoustic wave resonator 1, an interdigital transducer (hereinafter, referred to as IDT) 3 is formed on the upper side of a rectangular surface acoustic wave substrate 2. The IDT 3 has a pair of interdigital electrodes 3a and 3b. The interdigital electrode 3a has plural electrode fingers 3a1, and 3a2. The interdigital electrode 3b has plural electrode fingers 3b1 and 3b2. The electrode fingers 3a1, 3a2, and the electrode fingers 3b1, 3b2 are arranged so as to be inserted between each other in an interdigitated manner. In the edge reflection type surface acoustic wave device 1, the surface acoustic wave substrate 2 has a first edge 2a and a second edge 2b disposed opposite to each other. When an AC voltage is applied to the IDT 3, the SH type surface acoustic wave is generated. The SH type surface acoustic wave is propagated in the direction passing through the first edge 2a and the second edge 2b, and is reflected by the edges 2a, 2b. 
Accordingly, it is unnecessary to provide reflectors on the opposite sides of the IDT 3 in the surface acoustic wave propagation direction, so that the surface acoustic wave device can be miniaturized.
Further, in Japanese Unexamined Patent Publication No. 7-50538, an example of the method of producing an edge reflection-type surface acoustic wave device is described. The above-described prior-art production method will be explained with reference to FIG. 4.
First, a surface acoustic wave mother substrate 51 shown in FIG. 4 is prepared. Plural IDTs 53 are formed on one side main surface 51a of the surface acoustic wave mother substrate 51. The IDTs 53 correspond to the IDTs 3 of the edge reflection type surface acoustic wave resonators 1, respectively. In the case of the edge reflection type surface acoustic wave resonator, it is necessary to form a reflection edge from which a surface acoustic wave is reflected with very high precision.
Thus, according to the above-described prior art method, the first and second reflection edges are provided by forming cut grooves on the surface acoustic wave mother substrate 51 from one side main surface 51 a thereof after the IDTs 53 are formed. More concretely, cut grooves each having a width T shown in FIG. 4 are formed, for which a blade with a thickness T is used to form cut grooves 54A and 54B. In this case, the inner side walls of the grooves 54A and 54B which lie on the IDT 53 sides thereof constitute the first and second reflection edges, respectively. That is, in FIG. 4, the straight lines A1, A2, A3xe2x80x94and the straight lines B1, B2, B3xe2x80x94indicate the positions of the inner side walls on the IDT 53 sides of the above-described grooves 54A and 54B, that is, the positions of the first and second reflection edges, respectively.
As described in Japanese Unexamined Patent Publication No. 7-50538, it is necessary that the interval L, which is equal to the distance between lines B1 and A2, of the cutting lines along which the above-described surface acoustic wave substrate 51 is cut is set at a larger value than the thickness T of the blade. That is, it is described that the cut grooves 54A and 54B can be easily formed by setting L greater than T.
Further, according to the above-described prior art method, the cut groove 54A is formed along the cutting line A1 shown in FIG. 4, and thereafter, the cut groove 54B is formed along the cutting line B1. In this manner, the cutting is carried out along the cutting lines A1, B1, A2, B2, and A3 in that order, respectively. In particular, when the cutting process for forming the first and second reflection edges on the surface acoustic wave substrate 51 is carried out, a cutting device is fed sequentially from one end of the surface acoustic wave substrate 51 to the other end thereof in the direction passing through the first and second reflection edges.
However, when the cutting device is fed in the direction passing through the first and second reflection edges to carry out the above-described cutting, a feeding-quantity C by which the cutting device is fed for the next cutting along the cutting line B1 after the substrate 51 is cut along the cutting line A1, and a feeding-quantity D by which the cutting device is fed for cutting along the cutting line A2 after the substrate 51 is cut along the cutting line Bt are considerably different from each other. Thus, the cutting device can not be fed sequentially at an equal pitch for cutting. That is, it is necessary to carry out the cutting while the feeding-pitch of the cutting device is changed.
In this case, unless the feeding-quantities C and D are accurately controlled, the distances between the first and second reflection edges of the respective edge reflecting type surface acoustic wave resonators become different, and thereby, dispersions in resonance characteristic occur. Accordingly, it has been necessary to use an expensive cutting device with which the feeding-pitch can be easily changed, and moreover, the feeding pitch can be accurately set. In addition, the change of the feeding-pitch is very difficult, and the productivity is low.
It is possible that the surface acoustic wave substrate 51 is formed so that the above-described feeding quantities C and D become equal- to each other. However, if the feeding quantities C and D are equal, the portion of the surface acoustic wave substrate which becomes eventually unnecessary, that is, the surface acoustic wave substrate portion sandwiched between the cutting line B1 and the cutting line A2, is increased in size. Thus, the number of edge reflection type surface acoustic wave resonators which can be formed by use of the surface acoustic wave substrate 51 with a predetermined size is decreased and also, the productivity is reduced.
To overcome the problems described above, preferred embodiments of the present invention provide a method of producing an edge reflection type surface acoustic wave device, in which the process of forming reflection edges, carried out when individual edge reflection type surface acoustic wave devices are formed from a surface acoustic wave mother substrate, is improved, and many edge reflecting type surface acoustic wave devices can be efficiently produced with a high productivity.
According to one preferred embodiments of the present invention, the method of producing an edge reflection type surface acoustic wave device having first and second reflection edges opposed to each other preferably includes the steps of preparing a surface acoustic wave mother substrate having a plurality of IDTs formed on one surface side thereof, repeating the process of forming a cut groove on the surface acoustic wave mother substrate from one main surface side thereof whereby the first reflection edges of the respective surface acoustic wave devices are sequentially formed, and rep eating the process of forming a cut groove on the surface acoustic wave mother substrate from the one main surface side thereof whereby the second reflection edges of the respective surface acoustic wave devices are sequentially formed.
According to preferred embodiments of the present invention, since all of the distances between the first reflection end surfaces of adjacent end surface reflection type surface acoustic wave device portions and the distances between the second reflection end surfaces thereof are substantially equal to each other, the cutting can be carried out by feeding the cutting device or the surface acoustic wave substrate at an equal pitch in the process of forming the first reflection end surfaces and in the process of forming the second reflection end surfaces. Thus, the productivity is greatly improved, and moreover, the first and second reflection end surfaces are formed with high precision.
Accordingly, an end surface reflection type surface acoustic wave device which is inexpensive, has less dispersions in resonance characteristics, and has a high reliability is achieved.
It is preferable that in the process of forming the first reflection edges sequentially and in the process of forming the second reflection edges sequentially, a cutting device or the surface acoustic wave mother substrate is fed sequentially in the direction passing through the first and second reflection edges whereby the first or the second reflection edges are sequentially formed. The feeding-pitch of the cutting device and the surface acoustic wave mother substrate can be set to a constant value.
It is also preferable that the method further includes the step of rotating the surface acoustic wave mother substrate by 180 degrees about the axis passing through the centers of both the main surfaces of the surface acoustic wave mother substrate after the first edges are sequentially formed, whereby the second reflection edges are formed sequentially on the rotated surface acoustic wave mother substrate. The cutting device can be sequentially fed at an equal pitch to form the second reflection end surfaces after the first reflection end surfaces are formed. In addition, the first reflection end surfaces and the second reflection end surfaces can be formed via the same side of a cutting blade of the cutting device. Thus, an end surface reflection type surface acoustic wave device of which the resonance characteristic has minimal dispersions is achieved.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.